JPH0585742B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an air-fuel ratio control device for an internal combustion engine using a lean burn system.

Problems to be solved by conventional technologies and inventions In recent years, in addition to preventing exhaust pollution, efforts have been made to reduce fuel consumption.
A lean-burn system is used to operate the internal combustion engine at a lean air-fuel ratio. That is, a lean mixture sensor is provided in the exhaust pipe of the engine, and the output signal of the lean mixture sensor is used to feedback control the air-fuel ratio of the engine to an arbitrary value on the lean side. Lean mixture sensors measure the oxygen concentration of exhaust gas in this region because the oxygen concentration of engine exhaust gas and air-fuel ratio have a good correlation in the region of air-fuel ratio greater than the stoichiometric air-fuel ratio. This makes it possible to accurately detect the air-fuel ratio of the engine.

However, in the lean mixture sensor described above, the output changes depending on the surrounding back pressure. That is, as the atmospheric pressure decreases at high altitudes, the back pressure around the sensor decreases. Therefore, since the output of the lean mixture sensor is proportional to the oxygen concentration, at high altitudes the output of the lean mixture sensor decreases and the air-fuel ratio is determined to be rich, and air-fuel ratio feedback control proceeds and the air-fuel ratio becomes lean. Be on the side. As a result, the air-fuel ratio becomes leaner than the target lean air-fuel ratio, resulting in a problem that the engine misfires or surges.

Means for Solving the Problems In view of the above-mentioned problems, an object of the present invention is to prevent engine misfires or surging.
The means for doing so are shown in FIG.

In FIG. 1, the air-fuel ratio signal generating means detects the concentration of a specific component in the exhaust gas of an internal combustion engine and generates an air-fuel ratio signal Il indicating the air-fuel ratio of the engine.

The target air-fuel ratio calculation means calculates a target air-fuel ratio IRB according to predetermined operating state parameters of the engine. The atmospheric pressure detection means detects atmospheric pressure PM ₀ . The target air-fuel ratio correction means corrects the target air-fuel ratio IRB according to the detected atmospheric pressure PM ₀ . The feedback control means uses the above-mentioned air-fuel ratio signal Il to perform feedback control so that the air-fuel ratio of the engine converges to the corrected target air-fuel ratio IR.

Effect: Since the above-described configuration corrects the feedback target air-fuel ratio of the air-fuel ratio signal generating means (lean mixture sensor) according to the atmospheric pressure, it is possible to prevent the air-fuel ratio from shifting toward the lean side at high altitudes.

Embodiment FIG. 2 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 2, a pressure sensor 4 for detecting the absolute pressure of intake air in the intake passage 2 is provided in a surge tank 3 in an intake passage 2 of an engine body 1, and its output is sent to a multiplexer built in a control circuit 10. The signal is supplied to the A/D converter 101. Further, a throttle sensor 6 is provided on the shaft of the throttle valve 5 provided in the intake passage 2 of the engine body 1 for detecting whether or not the throttle valve 5 has a predetermined opening degree θ ₀ or more. This throttle opening θ ₀ is set at a value such that the internal pressure of the surge tank 3 is almost the same as atmospheric pressure, and when θ≧θ ₀ , the throttle sensor 6 generates an output signal LS (= “1”). do. Throttle sensor 6
The output signal LS of is supplied to the input/output interface 103 of the control circuit 10. Furthermore, a lean mixture sensor 8 is provided in the exhaust passage 7 of the engine body 1. Lean mixture sensor 8
If the atmospheric pressure is constant, the output of control circuit 1 can be obtained as a current output as shown in the output characteristics in Figure 3.
The voltage is converted into a voltage by a current-voltage conversion circuit 102 of 0 and then supplied to an A/D converter 101.

The distributor 9 includes a crank angle sensor 11 that generates a reference position detection pulse signal every 720 degrees in terms of crank angle, and a crank angle sensor 11 that generates a reference position detection pulse signal every 30 degrees in terms of crank angle. A crank angle sensor 12 is provided which generates a signal. These crank angle sensors 11, 12
The pulse signal is supplied to the input/output interface 103 of the control circuit 10, and the output of the crank angle sensor 12 is supplied to the interrupt terminal of the CPU 105.

Further, the intake passage 2 is provided with a fuel injection valve 13 for supplying pressurized fuel from a fuel supply system to the intake port for each cylinder.

The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, a current-voltage conversion circuit 102, and an input/output interface 10.
3. In addition to the CPU 105, a timer counter 106,
A ROM 107, a RAM 108, etc. are provided.
104 is a drive circuit for driving the fuel injection valve 13. The timer counter 106 includes, for example, a free run counter, a comparator register, an AND circuit that detects a match between the value of the free run counter and the value of the comparator register, and generates an interrupt signal. In addition, CPU1
The occurrence of interrupt 05 is caused by the A/D converter 101's A/D converter 101.
These include when the D conversion ends, when the input/output interface 102 receives a pulse signal from the crank angle sensor 12, when it receives an interrupt signal from the timer counter 106, etc.

The intake pressure data PM of the intake pressure sensor 4 and the output current value Il of the lean mixture sensor 8 are fetched by an A/D conversion routine executed at predetermined time intervals and stored in a predetermined area of the RAM 108. In other words, the data PM and Il in the RAM 108 are updated at predetermined intervals. Also, rotation speed data
Ne is calculated by an interrupt of the crank angle sensor 12 every 30° CA and stored in a predetermined area of the RAM 108.

The operation of the control circuit shown in FIG. 2 will be explained with reference to a flowchart.

FIG. 4 shows an atmospheric pressure calculation routine, which is executed at predetermined time intervals. In the present invention, atmospheric pressure is calculated using intake pressure. In step 401, it is determined whether the system is in a steady state. For example, the steady state is defined as whether the change in intake pressure |△PM| is greater than or equal to a predetermined value, or |PM−PMAV| (however, PMAV
The determination is made based on whether or not the calculated value (annealed value of the intake pressure) is greater than or equal to a predetermined value. If it is in a steady state, the process advances to step 402, and if it is not in a steady state, it jumps to step 408. In step 402, engine rotational speed data Ne is read from the RAM 108 and it is determined whether Ne<No, for example less than 3000 rpm. If Ne<No, proceed to step 403, and if Ne≧No, jump to step 408.

In step 403, the intake pressure correction amount is calculated using the one-dimensional map M1 based on the rotational speed Ne shown in FIG.
Calculate PMADD by interpolation. In step 404, LS=
“1” or not, that is, throttle valve opening θ≧θ ₀
Determine whether or not. If LS="1", then in step 405 _PM0 >PM+PMADD However, it is determined whether PM is intake pressure data and _PM0 is data corresponding to atmospheric pressure (hereinafter simply referred to as atmospheric pressure data). If PM ₀ > PM+PMADD, in step 407, PM ₀ ←PM+PMADD is set. This means that when the atmospheric pressure decreases as the driving vehicle moves to higher ground, the atmospheric pressure data
PM ₀ has been updated to be smaller. If PM ₀ ≦PM+PMADD in step 405, the process jumps to step 408.

On the other hand, in step 404, when LS=“0”, that is, throttle valve opening θ<θ ₀ , the step
Proceeding to step 406, it is determined whether PM ₀ ≦PM+PMADD. If PM ₀ ←PM+PMADD, then in step 407 PM ₀ ←PM+PMADD is set. That is, when the atmospheric pressure recovers as the driving vehicle moves from a highland to a lowland, the atmospheric pressure data PM ₀ is updated to increase.
If PM ₀ > PM + PMADD at step 406, the process jumps to step 408. In this way,
According to the routine shown in FIG. 4, atmospheric pressure data PM ₀ corresponding to atmospheric pressure is calculated based on the intake pressure data.

The calculation of the lean air-fuel ratio correction amount KLEAN will be explained with reference to the routine shown in FIG. step
In step 601, KLEANPM is calculated from the one-dimensional map based on the intake pressure data PM, in step 602, KLEANNE is calculated from the one-dimensional map based on the rotational speed data Ne, and in step 603
, calculate KLEAN←KLEANPM・KLEANNE. The calculated KLEAN is calculated in step 604.
The data is stored in RAM 108, and the routine ends at step 605. In other words, the lean air-fuel ratio correction coefficient is for setting the air-fuel ratio to the lean side.

The air-fuel ratio feedback control, that is, the calculation of the air-fuel ratio correction amount FAF will be explained with reference to the routine shown in FIG. The routine of FIG. 7 is executed at predetermined time intervals. In step 701, the latest lean air-fuel ratio correction amount KLEAN obtained in the routine of FIG.
The lean mixture sensor output target value IRB is calculated using the one-dimensional map M2 based on the following. In addition, 1
The dimensional map M2 is based on the graph of FIG.

In step 702, a correction amount K is calculated using a one-dimensional map M3 based on the latest atmospheric pressure data _PM0 obtained in the routine shown in FIG. In addition, 1
The dimensional map M3 is shown in FIG. In other words,
K means the IRB correction amount of the lean mixture sensor output target value due to a decrease in atmospheric pressure; therefore, K=1 in a lowland (760 mmHg).

In step 703, the lean mixture sensor output target value IRB is corrected by the correction amount K. That is, let IR←IRB×K be the lean mixture sensor output target value.

In step 704, it is determined whether a feedback condition is met. Feedback conditions include various conditions such as startup, cooling water temperature, etc. If the feedback condition is not met, proceed to step 712 and calculate the air-fuel ratio correction amount.
Let FAF be FAF←1. Conversely, if the condition is a feedback condition, the process advances to step 705 and air-fuel ratio feedback correction is performed.

In step 705, the lean mixture sensor 6
It is determined whether the output current value Il of is greater than or equal to the reference value IR. If Il≧IR, that is, when the air-fuel ratio is leaner than the predetermined lean air-fuel ratio, it is determined in step 706 whether or not it is the first lean side, that is, it is determined whether or not it is a change point from the rich side to the lean side. . As a result,
If it is the first lean side, FAF← in step 708
Add the skip amount A as FAF+A, and on the other hand,
If it is not the first lean side, then FAF in step 709.
←Add a predetermined amount a as FAF+a. In addition,
The skip amount A is set to be sufficiently larger than a. That is, A≫a.

In step 705, if Il<IR, that is, if it is richer than the predetermined lean air-fuel ratio, the process proceeds to step 707. In step 707, it is determined whether or not it is the cutest rich side, that is, it is determined whether it is a change point from the lean side to the rich side. As a result, if it is the first rich side, in step 710 FAF←FAF−
Subtract the skip amount B as B, and on the other hand, if it is not the first rich side, proceed to step 711, and FAF←
A predetermined amount b is subtracted as FAF-b. Note that the skip amount B is set to be sufficiently larger than b. That is, B≫b.

In other words, the control shown in steps 709 and 711 is called integral control, and the control shown in steps 708 and 711 is called integral control.
The control shown at 710 is called skip control. The air-fuel ratio correction amount FAF determined in steps 708 to 712 is stored in the RAM 108 in step 713, and this routine ends in step 714.

Next, in the case of an independent injection type, the fuel injection amount τ is calculated at each predetermined timing for each cylinder, and in the case of a simultaneous injection type, the fuel injection amount τ is calculated every 360° CA. That is, τ←τ _p・FAF・(1+KLEAN+K ₁ )K ₂ +K ₃ However, τ _p is the basic injection amount based on the intake pressure data PM and rotational speed data Ne. K ₁ , K ₂ , and K ₃ are other operating state parameters. This is the correction amount calculated by .

If it is an independent injection type, the injection start timing T _i is calculated and set in the injection start timing comparator register of the timer counter 106, and the injection end timing Te (=
By setting T _i +τ) in the comparator register for injection end timing, the timer counter 106
Fuel injection will be automatically performed by the interrupt processing from. Also, if it is a simultaneous injection type,
By generating an injection start signal to start injection and setting τ in the comparator register for injection end timing, fuel injection is automatically stopped by interrupt processing of the timer counter.

In the above embodiment, the IR correction coefficient K was calculated by finding the value PM ₀ related to atmospheric pressure from the intake pressure PM, but in the fuel injection system using the intake air flow rate detection method, the PM Q/Ne instead
Similar control is also possible using the value of (Q: intake air amount data). That is, it is also possible to obtain Q/Ne at a predetermined throttle opening and then apply IR correction from this value.

Effects of the Invention FIG. 10 is a graph for explaining the effects of the present invention. That is, in the past, as shown in B, the target air-fuel ratio A/F decreases as the atmospheric pressure decreases.
However, according to the present invention, as shown in A, even if the atmospheric pressure changes, the target can be maintained even if the atmospheric pressure changes. Correct A/F,
The control A/F can be made to match the target lean A/F correctly.

[Brief explanation of the drawing]

FIG. 1 is an overall block diagram for explaining the configuration of the present invention, FIG. 2 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an air-fuel engine according to the present invention, and FIG. Figures 4, 6, and 7 are flowcharts for explaining the operation of the control circuit in Figure 2, and Figure 5 is used for step 403 in Figure 4. FIGS. 8 and 9 are graphs for explaining the maps used in steps 701 and 702 of FIG. 7, and FIG. 10 is a graph for explaining the effects of the present invention. 1: Engine, 4: Pressure sensor, 5: Throttle valve, 6: Throttle sensor, 8: Lean mixture sensor, 10: Control circuit.

Claims (1)

[Scope of Claims] 1. A device that detects the oxygen concentration in exhaust gas of an internal combustion engine and generates an air-fuel ratio signal, which detects an air-fuel ratio signal where the relationship between the detected oxygen concentration and the air-fuel ratio is greater than the stoichiometric air-fuel ratio. an air-fuel ratio signal generating means having good correlation in a region; a target air-fuel ratio calculating means for calculating a target air-fuel ratio according to a predetermined operating state parameter of the engine; an atmospheric pressure detecting means for detecting atmospheric pressure; target air-fuel ratio correcting means for correcting the target air-fuel ratio to the rich side according to the detected atmospheric pressure when the air pressure decreases, and adjusting the air-fuel ratio of the engine using the air-fuel ratio signal. An air-fuel ratio control device for an internal combustion engine, comprising an air-fuel ratio feedback control means for performing feedback control so that the air-fuel ratio converges to a target air-fuel ratio. 2. The atmospheric pressure detection means includes an intake pressure detection means for detecting the intake pressure of the engine, a rotation speed detection means for detecting the rotation speed of the engine, and an intake pressure correction means for correcting the intake pressure by the rotation speed. a throttle valve opening determination means for determining whether the throttle valve opening of the engine is equal to or greater than a predetermined value; and when the throttle valve opening is equal to or greater than the predetermined value, the corrected intake pressure is the current atmospheric pressure. When the intake pressure becomes smaller than the current atmospheric pressure value, the atmospheric pressure value is updated with the corrected intake pressure, and when the throttle valve opening is less than the predetermined value, the corrected intake pressure is larger than the current atmospheric pressure value. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, further comprising: atmospheric pressure updating means for updating the atmospheric pressure value with the corrected intake pressure when the intake pressure becomes low. 3. The atmospheric pressure detection means includes an intake air amount detection means that detects the intake air amount of the engine, a rotation speed detection means that detects the rotation speed of the engine, and an intake air per rotation that calculates the intake air amount per one rotation of the engine. an intake air amount correcting means for correcting the intake air amount per revolution according to the rotational speed; and a throttle valve opening degree determining means for determining whether the throttle valve opening degree of the engine is equal to or greater than a predetermined value. , when the throttle valve opening is equal to or greater than the predetermined value and the corrected intake air amount per rotation becomes smaller than the current atmospheric pressure value, the corrected 1
Update the atmospheric pressure value according to the amount of intake air per rotation,
When the throttle valve opening is less than the predetermined value and the corrected intake air amount per rotation becomes larger than the current atmospheric pressure value, the corrected intake air amount per rotation increases the atmospheric pressure. An air-fuel ratio control device for an internal combustion engine according to claim 1, further comprising atmospheric pressure updating means for updating the value.